The invention relates to a turbo machine, especially a steam turbine having an inner housing and an outer housing spaced apart, so that a gap is formed between the inner housing and the outer housing.
It is known, as described in Published, Non-Prosecuted German Patent Application DE 35 22 916 A1 that during the operation of a turbo machine, especially a steam turbine, the inner housing, the outer.housing as well as the turbine rotor elongate to a different amount due to different temperatures acting on these parts. It is therefore normal practice to compensate for the difference in the axial elongation between the housings and the turbine rotor by translation related methods and/or devices. As the temperatures acting on the inner housing and the outer housing are also different, there may arise a temperature gradient in the inner housing and the outer housing which may lead to different deformations during operation of the turbo machine as well as during the cooling down of the turbo machine.
British Patent No. 740 944 relates to thermal turbines, more specially steam turbines, which contain an internal housing separated from an external housing by a gap. The turbine is driven by a driving medium, a part of which is branched off and passed through the gap between the internal and the external housing. During the operation of the turbine this part of the driving medium acts as a cooling medium for the external housing, so that the hot inner housing is thermally separated from the cold outer housing. Fins are secured on the inner face of the external housing in order to improve the heat transfer on the outer housing.
U.S. Pat. No. 5,388,960 relates to a forced-air-cooling apparatus of a steam turbine in a high temperature state just after an operation shut down of the steam turbine. This apparatus serves for safe and quick cooling of the turbine.
U.S. Pat. No. 3,746,463 relates to a multi-stage axial flow steam turbine having an inner and an outer casing. The inner casing is mounted within the outer casing in such a manner as to limit relative axial movement and allow free relative radial movement between the inner and outer casing, which is caused by changes in temperature. The inner casing therefore is mounted within the outer casing by a plurality of keys and keyways, fitted pins and axial alignment fits, is obtained by tongue and groove portions which locate the inner casing axially with respect to the outer casing and yet allow free radial movement of the inner casing with respect to the outer casing.
It is accordingly an object of the invention to provide a turbo machine with an inner housing and an outer housing which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which thermal deformations of the outer housing are smaller than a critical value.
With the foregoing and other objects in view there is provided, in accordance with the invention, a turbo machine having a main axis; an inner housing; an outer housing surrounding the inner housing forming a radial gap there-between; a top region disposed within the outer housing; and a bottom region disposed within the outer housing. A mounting region for mounting the inner housing on the outer housing is provided. A blading region extends along the main axis and is disposed within the outer housing. The radial gap has a narrowed part in the bottom region and the narrowed part extends along the main axis outside of the mounting region at least partially overlapping the blading region in a direction of the main axis.
The invention relies on the physical effect that during the shut down of the turbo machine the inner housing and the outer housing are at different temperatures. Due to the difference in temperature, a gaseous medium, like steam in the gap (space) between the inner housing and the outer housing is set in a thermal convection motion (temperature gradient driven flow) directed from the bottom region to the top region of the turbo-machine. This may lead to a temperature difference in the outer housing with a higher temperature in the top region as in the bottom region. Such a temperature gradient in the outer housing across the height of the outer housing may lead to a buckling of the outer housing (outer casing) from the top region to the bottom region. Under some critical conditions this may lead to a radial displacement of the inner housing and a rubbing of the moving blades of the rotor on the inner housing (inner casing).
The narrowing of the gap between the inner housing and the outer housing in the bottom region leads to a better transmission of heat from the inner housing to the outer housing as well as to a higher convection rate, especially a turbulent convection, in the top region. This leads to a super-linear temperature profile across the height of the outer casing. Therefore, the temperature profile in the outer casing has a temperature gradient (change of temperature per unit length AT/AH) in the bottom area which is greater than 1. The thermal stresses in the outer casing are therefore reduced, so that the chance of buckling of the outer casing along the main axis is reduced.
In accordance with another feature of the invention, the inner housing extends in the gap towards that outer housing, so that the gap, the space between inner housing and outer housing, is reduced along the main axis. The invention is also applicable for a turbine, in particular a steam turbine, having a blade region for the guide blades (vanes) instead of the inner housing or in addition to the inner housing.
In accordance with a further feature of the invention, a heat conducting extra mass is thermally coupled with the inner housing and situated in the bottom region. The extra mass may be of the same material as the inner housing. It is possible that the extra mass is part of the inner housing, especially cast as one piece together with the inner housing, welded to the inner housing or fastened to the inner housing in a suitable way. In accordance with an added feature of the invention, the extra mass or extra part of the inner housing may have approximately a triangular cross section, a rectangular cross section or another cross section which is suitable, according to the special geometry of the inner housing and outer housing as well as the physical parameters for the operation of the turbo machine.
The extra mass or extra part of the inner housing is preferably directed along the main axis and provides a rib or fin on the inner housing.
In accordance with an additional feature of the invention, a compensating mass is situated in the top region, in particular, the compensating mass is connected to the inner housing. The compensation mass leads to a contribution of mass of the inner housing, so that the center line of mass coincides with the main axis of the turbo machine. The compensation mass may have a similar shape as the extra mass so that a symmetry of the inner housing will be established. The compensating mass is also preferably directed along the main axis.
It is also in principle possible that the outer housing extends towards the inner housing in the bottom region to narrow the gap between inner housing and outer housing.
The turbo machinery is preferably a high pressure steam turbine or an intermediate pressure steam turbine.
In accordance with a further feature of the invention, the inner housing contains two housing parts that are separable from each other along a horizontal plain. Each housing part has preferably a horizontal radially outward directed flange. The housing parts are preferably mechanically fixed together through the flanges. For fastening the flanges together, commonly nuts and bolts or the like can be used. The flanges also reduce the gap between the inner housing and the outer housing in a horizontal plain between the top region and the bottom region. A convectional flow of steam from the bottom region to the top region or vice versa is in this case restricted. Under these circumstances a narrowing of the gap in the bottom region due to the narrow part is most effective, in the sense that heat transmission between inner housing and outer housing is improved and the temperature in the outer housing in the bottom region is raised.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a turbo machine with an inner housing and an outer housing, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.